1. Field of the Invention
The present invention relates to a device for preventing an outflow of a fuel vapor from a fuel tank.
2. Description of the Related Art
A fuel tank of a vehicle is normally equipped with a fuel inlet pipe extending upward from the fuel tank and used to replenish the fuel tank with fuel. In addition, the upper interior of the fuel tank is connected to the interior of the upper end portion of the fuel inlet pipe via a breather pipe, so that the fuel tank can be topped-up with fuel, by allowing the pressure in the fuel tank to escape via the breather pipe when the fuel tank is replenished. However, in this fuel tank, since the breather pipe is open to the outside air, the fuel vapor in the fuel tank escapes to the outside air via the breather pipe when the fuel tank is replenished.
Consequently, in order to prevent the escape of the fuel vapor to the outside air, devices are disclosed in which the breather pipe is connected to a charcoal canister containing activated carbon (for example, Japanese unexamined Pat. publications Nos. 61-132763 and 61-191427). In these devices, a solenoid valve is arranged in the breather pipe connecting the upper interior of the fuel tank to the charcoal canister, and this solenoid valve, which is normally closed, is opened when the fuel tank is replenished.
The fuel pump nozzle is normally equipped with a sensor which comes into contact with fuel moving upward in the fuel inlet pipe, to stop the replenishment of fuel. Consequently, if the breather pipe is arranged to extend at a level lower than the upper portion of the fuel inlet pipe, a problem occurs in that, when the replenishing operation is carried out, the fuel flows into the charcoal canister via the breather pipe and, in addition, the surface of the fuel in the fuel inlet pipe will not move upward. In order to eliminate such a problem, in the devices disclosed in the above-mentioned Japanese Unexamined Patent publications, a portion of the breather pipe between the upper interior of the fuel tank and the charcoal canister is arranged at a level higher than the upper end portion of the fuel inlet pipe so that, when the replenishing operation is carried out, the fuel in the fuel tank does not flow into the charcoal canister, and thus the surface of the fuel can move upward in the fuel inlet pipe.
However, when the fuel tank is arranged in a particular position on the vehicle body, for example, under a seat, it is difficult in practice to arrange the breather pipe so that it extends at a level higher than the upper end portion of the fuel inlet pipe.
In addition, in the devices disclosed in the above-mentioned Japanese Unexamined Pat. Publications, when the fuel tank is full, there is little or no space for air in the fuel tank, and thus, if the fuel in the fuel tank is heated by the hot outside air, a thermal expansion of the fuel occurs and the pressure in the fuel tank becomes extremely high, causing deformation of and damage to the fuel tank. Conversely, when a relatively large air space exists in the fuel tank, even if a thermal expansion of the fuel occurs, the pressure in the fuel tank is not increased. Therefore, to prevent the deformation of the fuel tank, it is necessary to allow the formation of a relatively large air space in the fuel tank when the fuel tank is replenished.